High-frequency signal-translating system



D 1 1 L. R. MALLING HIGH-FREQUENCY SIGNAL-TRANSLATING SYSTEM Filed March :5, 1942 w n u aaunpadm NQE INVENTOR LEONARD R.MALLING svfl/ Patented Dec. 14, 1 943 UNITED STATES 2,338,555 mon-ranoonncr sromn-mzmsmrmc ersrau Leonard lh-MallingrDouglastom N. Y., assignor to Hazeltin'e Corporation, a corporation of Delaware A pplication March 3', 1942, Serial No. 433,182

12 Claims.

' This invention relates to a high-frequency signal-translating system operable over a wide frequency range, and more particularly, to a coupling network included in such a system adapted for optimum signal translation over the range.

It is well known in the art to substitute in a high-frequency signal-translating system distributed inductance and capacitance for the lumped inductances and capacitances customarily employed in systems adapted to translate low-frequency signals. Thus, an oscillatory circuit, included in a high-frequency signaltranslating system, may comprise an oscillation generator to which is coupled an effectivelyresonant transmission line having a pair of parallel conductors of uniformly distributed inductance and capacitance and a short-circuiting member bridging the conductors and movable therealong for the purpose of tuning the resonant line to determine the resonant frequency of the oscillatin circuit. The resonant transmission line, plus its terminating impedance, is, generally, electrically equivalent to a line having a length equal to a quarter wave length of the resonant frequency of the resonant line and, hence, is effectively tuned to parallel resonance. Further, it-is well known in the art to derive energy from the resonant line in such an arrangement by way of a reactive coupling between the resonant line and an effectively-infinite transmission line to which is coupled a utilizing device. To thisend, the infinite transmission line generally includes a coupling loop spaced from and reactively coupled to a section of the resonant line affording a convenient means of translating highfrequency signals through the system. As employed throughout the specification, the term resonant transmission line" refers to a transmission line, plus its terminating impedance, which exhibits certain desirable characteristics at or near its resonant frequency which is determined by the distributed inductance and capacitance of the line and its terminating impedance.

In the aforedescribed arrangement, the coupling loop is frequency fixed with respect to the resonant line and, since the impedance per unit length of the resonant line varies with frequency, the resonant line and infinite transmission line are coupled with the desired coupling, that is,

,with matching impedances, at but one tuning condition. Energy loss is introduced into the system by poorly matched impedances and it would thus appear that, preferably, the transmission lines should be coupled with matched impedances throughout the operating frequency range.

Hence, this arrangement is unsuited for some high-frequency systems to bev operated over a wide frequency range. In some priorart arrangerangements, the coupling loop is movable with 5 respect to the resonant line, and ,with each adjustmentof the short-circuiting member to vary the tuning of the resonant line, the coupling loop is manually adjusted accordingly so -that the resonant line and infinite line are coupled with matching lmpedances for all conditions'of tunin'g.

Heretofore, it hasbeendiflicult to vary .the tuning and simultaneously adjust the coupling correspondingly so that arrangements of this. type have been inconvenient to operate over a wide frequency range.

' It is an object of the invention, therefore, to provide an improved, high-frequency signaltransl'atin system'including a coupling network, operable over a wide frequency range and which is not subject to one or more of the abovedescribed disadvantages of. the prior art arrangements. I 4

It is a further object of the invention to provide an improved. high-frequency signal-translating system operable over a wide frequency range including a coupling network comprising an effectively-resonant transmission lineand. an

effectively-infinite transmission line that are maintained reactively coupled with substantially the desired couplingas the resonantfrequency of the resonant line is varied over the operating range. As used in the specification and claims, the term desired coupling refers to that degree of coupling between the resonant transmission line and infinite transmission line that causes the latter to be terminated in its characteristic impedance.

In accordance. with the invention, a hightributed reactances, and a single control means for varying the tuning of the resonant line and for simultaneously varying the reactive coupling between the lines inversely with there'sonant frequency of the resonant line,'wher eby substantially the desired coupling is maintained between the lines asthe resonant frequency 'of the.

resonant line is varied over the operating range.

In a preferred embodiment of the invention, a

6Q high-frequency signal generator comprising a vacuum tube is included in the signal-translating system and an effectively-resonant transmiss on line, comprising a pair of parallel conductors having uniformly distributed inductance and capacitance and a movable short-circulting memher, is coupled to the vacuum tube. An effectively-infinite transmission line'having distributed reactance, and including a coupling loop movable in a plane at an angle to the plane-of the resonant line, is reactively coupled to the resonant line substantially solely by means of the foregoing distributed reactances, and a single control means is provided for moving the short-circuiting member to vary the tuning of the resonant line and for simultaneously moving the coupling loop of the infinite line to vary the eflective spacing between the coupling loop and the resonant line.

For a better understanding of the present invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing, and its scope will. be pointed out in the appended claims.

Fig. 1 is a circuit diagram, partially schematic, of a high-frequency signal-translating system embodying the present invention; Fig. 2 is a schematic circuit diagram which is electrically equivalent to a portion of the circuit of Fig. 1; and Fig. 3 comprises a family of curves representing the impedance characteristics of a resonant transmission line which is electrically equivalent to a line having a length equal to a quarter wave length of the resonant frequency of the line.

Referring now more particularly to Fig. 1, there is disclosed a high-frequency signal-translating system operable over a wide frequency range and embodying the present invention for the purpose of affording optimum signal translation over the range. Included in the system is a vacuum-tube oscillator I, represented schematically, having an anode, a cathode and a control electrode. An effectively-resonant transmission line 2 including distributed reactance is connected directly to the anode and control electrode of the vacuum tube so as to include in the line the effective inherent reactance associated with the electrodes and carried by the interelectrode capacitance Cg-p, the capacitance between the control electrode and anode of tube I. The resonant line 2 includes a pair of parallel conductors 3 and 4 which have uniformly distributed inductance and capacitance and a short-circuiting member bridging the conductors. This member comprises conductive elements 5 and 6 secured at their adjacent ends to an insulating strap 1. Near their opposite ends the elements 5 and 6 are apertured to receive, and be freely movable along, conductors 3 and I. A mica strip 8, positioned intermediate'the adjacent ends of elements 5 and 8, causes the short-circuiting member effectively to comprise a condenser II which completes the circuit of the resonant line for alternating currents and blocks from the control electrode the unidirectional potential supplied to the anode of tube I from a suitable source, indicated +B. A grid-leak resistor 9 is provided and a. condenser I is bridged across the terminals, of conductors 3 and 4 for a purpose to be described hereinafter. The conductive elements and 6 of the short-circuiting member are, preferably, brass blocks whereby the impedance of themember is very small.

The resonant transmission line Iis reactively coupled substantially solely by means of distributed reactance to an eflectively-innnite transmission line I! including distributed reactance and having a substantially uniform impedance-irequency characteristic. The infinite line Iii is positioned in a plane at an angle a to the plane of the resonant line 2 and comprises a movable section including parallel conductors II and I1 telescoping within conductive members It and IQ of a stationary section. The stationary section is held at an angle a with the plane of theresonant line by any convenient mechanical arrangement (not shown). A portion of the movable section is formed into a coupling loop 20 of a; length d comprising conductors 25 and 28 which are parallel to, but'spaced from, the conductors 3, 4 of resonant line 2. The eflectively-infinite line it is in this manner reactively coupled by means of loop 20 to resonant line 2. The infinite line I5 is terminated at its opposite ends in its characteristic impedances 2| and 22, the former being included within the coupling loop 20. The latter, which represents a suitable load connected to the line such as a transmitting antenna, terminates the other end ofthe line. Aillxed to the coupling loop 20 is a suitable nonconductive and nonmagnetic supporting block 23,

- freely slidable upon or properly geared to a vertically projecting guide post 24 secured to the strap 1 and comprising therewith a single control means, whereby the short-circuiting member may be advanced along the conductors 3 and l and the movable section of the infinite line II moved simultaneously to vary the effective spacing between the coupling loop 20 and the resonant line 2. The broken-line construction represents the relative positions of the resonant line 2 and coupling loop 20 with the short-circuiting member 5, 6, 1 advanced along conductors 3 and 4 toward the tube l.

It maybe seen that the arrangement Just described comprises a lush-frequency oscillation generator including a vacuum tube l and a tuned circuit 2 which is connected between the anode and control electrode of the tube. The cathode of tube I is effectively connected to the mid-point of the tuned circuit and, thus, the oscillation generator is of the type represented schematically in Fig. 2, wherein the distributed inductance of the conductors 3 and 4 of the resonant circuit 2 is represented by the lumped inductances La and L4 and the interelectrode capacitance Cg-p and distributed capacitance of the resonant circuit 2 are represented by the lumped capacitance C. The capacitance C's represents the blocking condenser ll, comprising elements 5, 8, and I, which blocks the anode operating potential from the control electrode. The oscillating circuit of Fig. 2 is generally similar to the well-known Hartley type of oscillator, the operation of which is well understood in the art and need not be repeated.

In the arrangement of Fig. 1, the frequencydetermining circuit of the oscillator, that is. the effectively-resonant transmission line 2 plus its terminating impedance. is electrically equivalent to a quarter wave length line of the resonant frequency of the tuned circuit and has an impedance-length characteristic of approximately sinusoidal shape, as indicated by the curves of Fig. 3. With the short-circuiting member in its most remote position from tube I, the resonant line is tuned to a frequency A, its lowest tuning frequency, and the impedance along the line 2,330,055 varies from a minimum at the shortcircuitin member 5, 6, 8 to a maximum at the opposite terminals of the line 'or at the electrodes of tube to which the resonant line is coupled. The maximum value of the impedance is made substantially equal to the anode-grid impedance of thegenerator I for maximum strength of oscillations. advanced along the conductors 3 and 4 toward the tube l, the resonant line 2 is tuned to progressively higher frequencies, such as f2 and fa, and the impedance characteristic varies with frequency as indicated by the curves of Fig. 3.

The impedance. of a section of the resonant line of length d at a given distance from the short-circuiting member increase as the shortcircuiting member is advanced along conductors 3 and l to turie the resonant line to higher frequencies, as represented by the intersection of the ordinate line d-d in Fig. 3, with the curves f1, f2, and fa. Hence, when a coupling section of a constant length is employed to couple the transmission lines, unless the coupling is varied with frequency, as is contemplated by the invention, or unless som other method of compensation is employed, the resonant line 2 and the infinite line I are coupled with matching impedances at but one frequency and loss is introduced into the system when signals of other frequencies are translated.

-In accordance with the above-described embodiment of the invention, however, as the shortcircuiting member is moved along the conductors 3 and 4 for the purpose of varying the tuning of the resonant line over the operating range, the movable section of the infinit line I5 is moved simultaneously and, since it moves in a plane at an angle to the plane of the resonant line, the effective spacing between the lines is varied, thereby effectively to vary the reactive coupling between the lines inversely with the resonant frequency of the resonant line and so that substantially the desired coupling is maintained between the lines as the resonant frequency of the resonant lin is varied over the operating range.

To establish optimum operating conditions of the system disclosed in Fig. 1, the effectively-infinite transmission line I5 i located at such an angle a with respect to th effectively-resonant transmission line 2 that when the short-circuiting member is placed in its extreme position from tube I, tuning the resonant line-to its lowest frequency, the resonant line 2 and the infinite line l5 are coupled with matching impedances, and so that, as the short-circuiting member is advanced towards tube l, tuning th resonant line to progressively higher frequencies, the movable section of the infinite line I5 is moved simultaneously to vary the effective spacing between the lines, thereby effectively to reduce the coupling between the lines inversely with frequency so that the lines remain coupled with substantially matching impedances as the resonant frequency of the resonant line is varied over the operating range.

The condenser l0, connected across the extremities of the conductors 3 and 4 most remote to tube I, is provided to prevent tuning of that portion of the conductors 3 and 4 positioned to the right of the short-circuitin member to any frequency within the tuning range of the apparatus.

While applicant does not intend to limit the invention to any specific circuit constants, the

As the short-circuiting member is.

following circuit constants are given as illustrative of a specific embodiment of the invention:

Tube l No. 368A Conductors 3 and l A; inch brass rods spaced of an inch apart, length-6 inches V inch brass rods spaced Conductors l6 and l| of an inch apart While the coupling loop 20 has been disclosed as being parallel to the plane of the resonant line 2, it is to be understood that this is not an essential limitation and, if desired, the coupling loop may be positioned in a plane parallel to the plane of the infinite line l5. It is to be further understood that the length of the resonant line 2 need not necessarily be the electrical equivalent of a line having a length equal to a quarter wave length of the operating frequencyfbut may, if desired, be any odd multiple thereof, since it is well known that, when a short-circuited transmission line is electrically equivalent to a line having a length equal to an odd multiple of quarter wave lengths of its excitation signal, it exhibits the impedance characteristics disclosed in Fig. 3. Further, while the arrangement of Fig.

1 is directed to the translation of generated highfrequency signals from the-resonant line 2 to the transmission line IS, the principles and concepts of this invention are equally useful in a highfrequency device wherein high-frequency signals are applied from the effectively-infinite transmission line IE to the effectively-resonant transmission line 2 for utilization by a device to which the resonant line is coupled.

It is also well known in transmission network theory that a short-circuited transmission line, which is electrically equivalent to a line having a length equal to a half wave length of its exciting signal, has an impedance characteristic analogous to that of a series-resonant circuit. It may be seen, therefore, that the resonant line may be electrically equivalent to a line having a length equal to a half wave length of its resonant frequency when it is desired to couple the resonant line to a low-impedance device, and inthis arrangement a coupling network embodying the principles of this invention, namely, the feature of adjusting the coupling between the resonant line and an infinite line coupled thereto, is equally applicable to afford optimum signal translation over a wide frequency range. Further, the coupling loop in such an arrangement may be terminated in a short circuit, since at series resonance a transmission line has a minimum impedance.

An open-circuited section of a transmission line which is electrically equivalent to a line having a length equal to a half wave length of its resonant frequency exhibits the same impedance characteristic as a short-circuited section electrically equivalent to a line having a length equal to a quarter wave length of 'its resonant frequency. Similarly. the impedance characteristic of an open-circuited section of a transmission line electrically equivalent to a line having a length equal to a quarter wave length of its resonant frequency is substantially the same as that of a short-circuited section which is electrically equivalent to a line having a length equal to a half wave length of its resonant frequency. Thus, it becomes apparent that any of these equivalent sections may readily be employed in a transmission system utilizing this invention.

While there has been described what is at present considered to be the preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A high-frequency signal-translating system operable over a wide frequency range comprising,

an effectively-resonant transmission line including distributed reactance, an effectively-infinite transmission line including distributed reactance and reactively coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for varying the tuning of said resonant line and for simultaneously varying the reactive coupling between said lines inversely with the resonant frequency of said resonant line, whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

2. A high-frequency signal-translating system operable over a wide frequency range comprising, a short-circuited effectively-resonant transmission line including distributed reactance, an effectively-infinite transmission line including distributed reactance and reactively coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for varying the tuning of said resonant line and for simultaneously varying the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

3. A high-frequency signal-translating system operable over a wide frequency range comprising, an effectively-resonant transmission line including distributed reactance and electrically equivalent to a line having a length equal to an integral multiple of quarter wave lengths of the resonant frequency of said line, an effectivelyinfinite transmission line including distributed reactance and reactively coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for varying the tuning of said resonant line and for simultaneously varying the reactive coupling be-' tween said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

4. A high-frequency signal-translating system operable over a wide frequency range comprising, an effectively-resonant transmission line including distributed reactance, a transmission line including distributed reactance and effectively terminated in its characteristic impedances and reactively coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for varying the tunin of said resonant line and for simultaneously varying the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

5. A high-frequency signal-translating system operable over a wide frequency range comprising, an efiectively-resonant transmission line including distributed reactance, an effectively-infinite transmission line including distributed reactance and spaced from but reactively coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for varying the tuning of said resonant line and for simultaneously varying the effective spacing between said lines effectively to vary the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

6. A high-frequency signal-translating system operable over a wide frequency range comprising, an effectively-resonant transmission line including distributed reactance, an effectively-infinite transmission line including distributed reactance and reactively coupled to said resonant line substantially solely by means of said distributed reactances and having a portion movable in a plane at an angle thereto, and a single control means for varying the tuning of said resonant line and. for simultaneously moving said infinite line in said plane to vary the effective spacing between said lines thereby effectively to vary the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

7. A high-frequency signal-translating system operable over a wide frequency range comprising, an effectively-resonant transmission line including distributed reactance, an effectively-infinite transmission line including distributed reactance and positioned in a plane at an angle to said resonant line and having a movable section reactively coupled to said resonant line substantially solely by means of said distributed reactances,

and a single control means for varying the tuning of said resonant line and for simultaneously moving said section of said infinite line effectively to vary the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

8. A high-frequency signal-translating system operable over a wide frequency range comprising, an effectively-resonant transmission line including distributed reactance, an effectively-imfinite transmission line including distributed reactance and including a coupling loop reactively coupling said lines substantially solely by means of said distributed reactances, and a single control means for varying the tuning of said resonant line and for simultaneously varying the reactive coupling between said coupling loop and said resonant line inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said coupling loop and said resonant line as the resonant frequency of said resonant line is varied over said range.

9. A high-frequency signal-translating system operable over a high-frequency range compris-- ing, an effectively-resonant transmission line including distributed reactance and including a pair of parallel conductor and a short-circuiting member movable along said parallel conductors, an effectively-infinite transmission line including distributed reactance and coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for moving said short-circuiting member to vary the tuning of said resonant line and for simultaneously varying the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

10. A high-frequency signal-translating system operable over a wide frequency range comprising, an efiectively-resonant transmission line including distributed reactance and having an impedance characteristic variable with the tuning of said line, an effectively-infinite transmission line including distributed reactance and having a substantially constant impedance and reactively coupled to saidiresonant line substantially solely by means of said distributed reactances with the impedances of said linesmatching, and a single control means for varying ,thetuning of said resonant line and for simultaneously varying the reactive coupling between said lines inversely with the resonant frequency of said resonant lines whereby said lines remain eflectively coupled with substantially matching impedances as the resofor simultaneously varying the reactive coupling between said lines inversely with the resonant frequency of said resonant line whereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

12. A high-frequency signal-translating system operable over a wide frequency range comprising, a vacuum tube having a pair of electrodes associated with which there is an effective inherent reactance, an effectively-resonant transmission line including distributed reactance and coupled to said eleotrodesso that said inherent reactance is eiiectively included in said line, an eflectivelyinfinite transmission line including distributed reactance and reactively coupled to said resonant line substantially solely by means of said distributed reactances, and a single control means for varying the tuning of said line and for simultaneously varyingthe reactive coupling between said lines inversely with the resonant frequency of said resonant linewhereby substantially the desired coupling is maintained between said lines as the resonant frequency of said resonant line is varied over said range.

LEONARD R. MAILING. 

